Lets view this in order.
Jesus ask the disciples, who think that I am? and then Peter said Christ, the Son of the living God.
Upon this conffession Jesus blessed him and gave keys of the kingdom of heaven.
Then Jesus announces how the Son of Man should suffer from the elders and chiefs, Peter then criticize Jesus saying ...
First of all, St. Peter repented or turned back from his denial, according to the prophecy of Christ:
Luke 22:32 (DRB) And the Lord said: Simon, Simon, behold Satan hath desired to have you, that he may sift you [all] as wheat: 32 But I have prayed for thee, that thy faith fail not: and thou, being once converted, confirm thy brethren. 33 Who said to him: ...